In the recycling of scrap metal, the electric arc furnace process, in which the scrap metal is melted by forming electric arcs between graphite electrodes and the scrap metal, is commonly used. High quality steels can be made by this process. However, during the recycling process, zinc and other non-ferrous metals, present in the scrap metal, as well as some of the iron, are "evaporated" forming minute particles of the oxides of these metals. These particles settle as dust in the electric arc furnace flues. The dust is unsuitable for recycling due to the buildup of the non-ferrous content which has a deleterious effect on the steel produced. Typically, the dust contains about 25 per cent zinc, 25 per cent iron, 5 per cent lead, some tin, cadmium, chromium and copper, the remainder being silica, lime and alumina.
The disposal of this dust has become a major problem for steel producers as, due to the strict environmental legislation in countries such as Canada and the U.S., the dust can no longer be simply disposed of as landfill because of the constant danger of the toxic or hazardous metal components thereof, such as lead, chromium and cadmium, being leached out by rain or underground water to contaminate rivers, lakes and other natural resources. Hence, the treatment of the dust to remove the hazardous or toxic metals therefrom so that it can safely be used as landfill has become a priority. In order to carry out the treatment on an economical basis, an effort has been made to render the process feasible by remarketing of the non-ferrous metals removed from the dust during treatment, notably zinc and, to a lesser extent, lead. However, efforts in this direction have so far not been entirely successful.
It is accordingly an object of the present invention to provide a process for the treatment of EAF dust which is economically feasible.